This invention relates to a fuel injection system, and more specifically to an injection system capable of preventing abnormal operations such as secondary or non-uniform fuel injection.
A conventional fuel injection system, as shown in FIG. 1, comprise a cam 1, an injection pump 2, a delivery valve 3, an injection pipe 4, a nozzle holder 5, and a nozzle 6.
Injection system made up of these components are known to undergo, during their operation, more or less fuel pressure fluctuations as typically represented in a graph in FIG. 2 which originally appeared in "New Handbook for Automotive Engineers " (edited by Society of Automotive Engineers of Japan, Inc.). Of the pressure-fluctuating factors, the reflection waves indicates at W are primarily responsible for the abnormal injection.
The mechanism for developing the reflection waves W is as follows. At the end of fuel injection a recess 23 of the plunger 21 communicates with a fuel port 24 of the pump barrel 22 to release the fuel pressure. A needle valve 61 is consequently forced by a spring 62 to close the nozzle orifice 63. At this point, the delivery valve 3 acts to suck the fuel back, so that the fuel pressure drops from the maximum P.sub.1 to the minimum P.sub.2 level within a very short period of time. This drastic pressure change is transmitted to and from the nozzle 6 to produce reflection waves W.
If the amplitude of the reflection wave motion is so wide that the valve opening pressure P.sub.3 is exceeded as indicated by a broken line in FIG. 2, the needle valve will again be opened for irregular fuel injection. Also, if the reflection wave is not appropriately damped and a proper residual pressure P.sub.4 is not maintained, hunting or knocking may result.